Conventionally, as a vibratory actuator having a piezoelectric element, one which is disclosed in Patent Document 1 is known.
The vibratory actuator of Patent Document 1 includes an actuator body including a piezoelectric element and two driver elements attached to the actuator body.
The actuator body includes a plate-like piezoelectric element having a longitudinal direction. By applying alternating currents having different phases to two pairs of diagonally opposite electrodes, a longitudinal vibration (so-called an expanding/contracting vibration) in a longitudinal direction of the piezoelectric element and a bending vibration in a lateral direction of the piezoelectric element are induced in a coordinated manner. As a result, the driver elements perform an orbital motion, more specifically, an elliptical motion in a plane including the longitudinal direction and the lateral direction of the piezoelectric element.
The two driver elements, which are in the form of substantially a hemisphere, are provided on a long side surface of the actuator body. The long side surface faces in the vibration direction of the bending vibration of the actuator body, and is bent and deformed in accordance with the bending vibration performed by the actuator body. In other words, the long side surface of the actuator body undulates. The two driver elements are attached to an antinode of the bending vibration of the long side surface where the bending displacement is maximum.
The vibratory actuator thus configured is provided between a stationary body, and a movable body which can be moved relative to the stationary body. Specifically, the vibratory actuator is fixed to one of the stationary body and the movable body while the driver elements abut on the other (also referred to hereinafter as an abutment body) of the stationary body and the movable body. In this state, when the vibratory actuator is activated to cause the driver elements to perform the orbital motion as described above, the driver elements orbit while pressing themselves against the abutment body to increase a friction force in a zone of the orbital motion, and orbits while being apart from the abutment body or with the friction force between the driver elements and the abutment body being reduced in another zone of the orbital motion. When the driver elements orbit while pressing themselves against the abutment body, a driving force is transmitted to the movable body by means of the friction force between the driver element and the abutment body, whereby the movable body is driven in a predetermined direction.
In this case, the actuator body is biased by a biasing member in a direction in which the driver elements are pressed against the abutment body, whereby the friction force between the driver elements and the abutment body is increased. As a result, the driving force of the actuator body is efficiently transmitted to the movable body. Specifically, the biasing member is provided on a surface of the actuator body opposite to the surface on which the driver elements are provided. The biasing member biases the actuator body toward the abutment body.
Citation List
Patent Document
Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-304963